This is a use of the spyglass client-side-imagemap stuff.
The documentation is at:
"A Proposed Extension to HTML : Client-Side Image Maps",
James L. Seidman, 09 Nov 1995.
<draft-seidman-clientsideimagemap-01.txt>
http://www.ics.uci.edu/pub/ietf/html/draft-seidman-clientsideimagemap-01.txt
Abstract
The markup language known as "HTML/2.0" provides for
image maps. Image maps are document elements which allow
clicking on different areas of an image to reference different
network resources, as specified by Uniform Resource Locators
(URIs). The image map capability in HTML/2.0 is limited in
several ways, such as the restriction that it only works with
documents served via the "HTTP" protocol, and the lack of a
viable fallback for users of text-only browsers. This document
specifies an extension to the HTML language, referred to as
"Client-Side Image Maps," which resolves these limitations.
which is linked from:
"IETF HyperText Markup Language (HTML) Working Group"
http://www.ics.uci.edu/pub/ietf/html/
which is linked from:
"HyperText Markup Language (HTML)"
http://www.w3.org/pub/WWW/MarkUp/
which is linked from:
"The World Wide Web Consortium"
http://www.w3.org/
I suspect folks have no problem finding the HTML page on www.w3.org,
but following the link to the IETF WG page is a bit of magic that not
many folks know, I suspect.
On our HTML page, under "Related Resources," you might guess to follow
the link to Yahoo; there, you might search for Map. Hmmm... no joy.
It's been suggested that we maintain a reference guide of HTML
elements, attributes, entites, etc. This stuff changes fast, so
it's difficult. Also, it's difficult to keep track of the proposals
without endorsing them before they've been through the appropriate
consensus processes.
One document that does a good job is:
HTML Reference Manual
http://www.sandia.gov/sci_compute/html_ref.html
Michael J. Hannah, Sandia National Laboratories <mjhanna@sandia.gov>
I just added a link to that reference from our HTML page. Enjoy.
Dan